Retroreflective articles are employed for various safety and decorative purposes. One type of retroreflective article includes small beads or spheres, typically made of transparent to semi-transparent glass. The beads have a reflective material positioned at a rear surface. Incoming light enters the front surface of the beads, refracts at the front surface, reflects off the reflective material at the rear surface and back toward the front surface, and refracts out of the front surface back toward the light source.
Reflective materials are conventionally deposited at the rear surface of the beads in one of two manners; either as a continuous layer that is separate and apart from the beads, or as a coating on the rear outer surface of the beads.
Various problems are associated with these conventional methods. Specifically, when a reflective layer is formed separate and apart from the beads, the separate layer is not conformed to the curved rear surface of the beads, but remains as a flat reflective surface. Such flat reflective surfaces fail to provide the desired retroreflective fill factors necessary for certain applications.
Further, coating a reflective layer directly on the rear surface of the beads introduces orientation problems when applying the beads to a substrate. In particular, the beads have to be positioned on a substrate in a manner so that the front surface of the beads which is free of coating, is directed away from the substrate and toward the light source. Often intricate processing steps and specialized equipment are required to provide such proper orientation of the spheres on the substrate. Additionally, such coating processes often involve vapor deposition of a metal onto the rear surface of the spheres, which further increase the cost and time associated with forming retroreflective articles. More complex orientation problems arise when trying to attach the coated beads to a surface that is not flat and planar. Often, retroreflective films are used for this purpose. In such methods, when attempting to apply a flat film containing a layer of the coated spheres onto a contoured surface, the film does not lay smoothly on the object, and tends to fold and crease, thus resulting in decreased retroreflective efficiency for the films.